1. Field of the Invention
The present invention generally relates to a pixel structure and a manufacturing method thereof. More particularly, the present invention relates to a pixel structure and a manufacturing method thereof having a pixel storage capacitor comprising at least three layers of transparent capacitance electrodes.
2. Description of Related Art
Conventionally, a thin film transistor (TFT) liquid crystal display (LCD) is constructed by TFT array substrate, color filter array substrate and liquid crystal layer. The TFT array substrate is constructed by a plurality of array arranged pixel structures. Each pixel structure includes a thin film transistor (TFT), pixel electrodes and a pixel storage capacitor. The TFT includes gate, channel, drain and source, and is applied as the switching component of liquid crystal display unit. For example, when the pixel electrode is at selecting state (i.e., at “ON” state), the signal is written to the pixel. Alternatively, when the pixel electrode is at non-selecting state (i.e., at “OFF” state), the pixel storage capacitor is maintained at the voltage level for driving the liquid crystal. Therefore, the performance of the liquid crystal display (LCD) is highly dependent on the capacitance of the pixel storage capacitor.
Generally, the pixel storage capacitor of the conventional pixel structure is constructed by a first metal layer (metal 1), a second metal layer (metal 2), a dielectric layer between the first and second metal layer and pixel electrodes. When the pixel storage capacitor is disposed on the gate, it is called Cst on gate, and when the pixel storage capacitor is disposed on the common line, it is called Cst on common. Generally, the gate or the common line (i.e., the first metal layer) is used as an electrode, and the second metal layer and the pixel electrode that are electrically connected with each other are used as another electrode. However, the electrode of the conventional pixel storage capacitor is generally composed of non-transparent metal material. Therefore, the aperture ratio of the pixel structure decreases when the pixel storage capacitor increases, and the brightness of the liquid crystal display (LCD) is also decreased.
In order to solve the problems due to decrease in the aperture ratio, another conventional pixel structure is also developed. FIG. 1 is cross-sectional view schematically illustrating a conventional pixel structure. Referring to FIG. 1, the pixel structure 100 is disposed on the substrate 110, wherein the pixel structure 100 includes a scan line (not shown), a data line 130, an active component 140 and a pixel storage capacitor 150. The scan line and the data line 130 are disposed on the substrate 110. The active component 140 is disposed on the substrate at the intersection of the scan line and the data line 130 and electrically connected to the scan line and the data line 130. The pixel storage capacitor 150 includes a pixel electrode 152 and a transparent capacitance electrode 154, wherein the pixel electrode 152 is electrically connected to the active component 140.
Since the pixel electrode 152 and the transparent capacitance electrode 154 of the pixel storage capacitor 150 are composed of transparent materials, the aperture ratio of the pixel structure 100 is not reduced due to the pixel storage capacitor 150. However, in a high resolution liquid crystal display (LCD), the area of the capacitance electrode is reduced, thus the capacitance of the pixel storage capacitor 150 that has only two layers of capacitance electrodes is not sufficient. In order to increase the capacitance of the pixel storage capacitor 150, if the distance between the pixel electrode 152 and the transparent capacitance electrode 154 is reduced, the fabrication of the dielectric layer is not easy.